Characterization and isolation of a rotifer-deterrent compound in the red tide dinoflagellate Karenia brevis

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Spontaneous phytoplankton blooms cause extensive damage to aquatic ecosystems all over the world. Red Tide, a type of bloom, causes extensive damage in the Gulf of Mexico every year. Red tide is caused by Karenia brevis, a type of phytoplankton known to be especially hazardous because of the harmful toxins it secretes into its environment. Although this phytoplankton species, like many others, can cause extensive environmental damage, little is known about its eco-system dynamics. Studying the relationships between phytoplankton and their consumers will help to better understand the mechanisms of bloom formation. For instance, previous research has demonstrated that Karenia brevis deters feeding for a potential grazer, the rotifer Brachionus plicatilis. Further research showed that a cellular component may be responsible for defending K. brevis against grazers. Using bioassay- guided fractionation techniques, we have attempted to isolate and characterize the chemical responsible for this deterrence. Liquid partition yielded a deterrent, lipophilic fraction . Size- exclusion chromatography also generated an active fraction, by separating compounds by molecular size. By characterizing this unknown compound, we hope to learn more about the interactions between phytoplankton and their consumers.